[FieldTrip] changed channel names for EGI data format from 'e' to 'E'
r.oostenveld at donders.ru.nl
Tue May 3 10:20:05 CEST 2011
Dear fieldtrip users working on EGI data,
The EGI system does not have well described channel names, but most software deals with it by prefixing the EGI channel names with an 'E', e.g. E1, E2 ... E256
It turned out that there were some inconsistent definitions whether it should be a lowercase 'e' or an uppercase 'E'. After consulting with some EGI experts (Joseph Dien, Catherine Poulsen, Ingrid Nieuwenhuis), I have just changed fieldtrip to use an uppercase 'E' consistently throughout the code. The EGI layouts (*.sfp files) also use this uppercase definition.
The consequence is that string comparisons between channels like 'e1' and 'E1' might fail and that in the analysis (e.g. grandaveraging data with mixed case labels) the identical channels are not recognized/matched to each other. If you encounter problems like these, you should fix them by converting the channel labels for data that you have stored on disk in *.mat files to uppercase. That can be easily done with the "upper" function in MATLAB for example like this:
data.label = upper(data.label);
timelock.label = upper(timelock.label);
freq.label = upper(freq.label);
freq.labelcmb = upper(freq.labelcmb);
Sorry for the inconvenience that this causes, hopefully in the future with the consistent definition of the channel labels we won't have problems like this any more.
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